Means for preventing bias in telegraph systems



Dec. 5, 1933. J. CLARKE 1,937,640

MEANS FOR PREVENTING BIAS IN TELEGRAPH SYSTEMS Filed Oct. 4, 1952 W 0 0'0 0 0 0 Wm INVENTOR JZ. Clarke ATTORNEY Patented Dec. 5,1933

UNITED- STATES:

MEANS, FOR. PREVENTING- BIAS. IN, I TELEGRAPH SYSTEMS 6. Claims, (01. 178;-6 6) This invention relates to means for preventing bias; in telegraph signaling, and has for its purpose the. elimination of such bias as arises in connection with the time of travel of a sending device between its marking and spacing positions.

Most telegraph systems employing current and no-current elements for the transmission of telegraph signals, especially in the case of carrier frequency systems, are subject to the lengthening either of each spurt of current, or of the interval between spurts, depending upon the method of keying by an amount equal to the travel time of the sending device. Although this effect may not be serious at ordinary speeds it becomes relatively large at comparatively high speeds. In this invention I propose to. eliminate such biasing effects or to reduce them to so low a, value as to be negligible even at such high speeds as 400 or 500 words per minute.

The invention will be better understood by reference to the following specification and accompanying drawing, in which Figure 1 shows the circuit arrangement for the transmitting end of a carrier frequency telegraph system, em;- bodying my invention. Fig. 2- is a modification thereof as applied to direct current telegraph signaling. Figs. 3 and 4 show certain types of networks which are represented symbolically in Fig. 1.

Referring more specifically to Fig. 1, there is shown at S a source of carrier frequency-cup. rent, such as a 5000 cycle source. Ordinarily this would be connected directly to a transmission line L through any suitable sending device which-moves alternately from marking to spacing position. In such a connection, when in series, it is apparent that the voltage from-the high frequency source is removed from the line 4Q as soon as the sending device leaves the marking position, and remains off not only while the sending device is at spacing position, but also during the time of to and fro travel of the sending device. When the sending device is in shunt across the line the reverse occurs; that is the marking time is increased. This biasing of the signals, which becomes serious at high speeds, is the feature which I wish to eliminate. Attempts have been made to reduce the effect by biasing the sending device in one way or another, but I have found these uncertain in action and therefore unsatisfactory.

In my invention I make connection from the high frequency source to the line through 'a 'vacuum tube of the three-electrode type as shown at 6, this tube preferably operating on a reason .ably flat portion of its characteristic, in other words, acting as a. good repeater or amplifier, Across the grid circuit, of the-tube are connected in seriesv resistances. 3v and 9 and biasing battery T60.

11. The resistance 8 is of relatively small mag nitude, say 50,000 ohms, but, the resistance 9, is considerably larger, such as 500,000 ohms. Across the resistance 9 is connected a condenser 14 which may beof the order of one-microfarad'. 65.

In addition to the biasing batter-y11-I provide biasing batteries 16 and 1'1, oppositelypoled, one or the other of which may be connected virtually in series with the biasingbattery 11, this being accomplishedby means of a connection con--70,

trolled by the sendingdevice 19 which comprises a relay winding 20 and a member 21' movable. from marking to spacing position'under control of the winding 20. In the spacing position the battery 16 is connected, in series with the battery 11, and in such direction as to increase the negative bias of the tube grid, and under this condition the bias will be sufficiently high to block or substantially block the plate current of the tube. In its marking position, however, the bat- 8Q. tery 1,7 is introduced, and in opposition to the battery 11. The resultant bias of. the grid is 1 thus suificiently reduced so thatcarrier fr'equency voltage from. the source S is repeated in the plate circuit of the tube and sent out on 5 the. line L. p

At the time thatthe one or the other of the batteries 16 and, 17 is connectdiin circuit, the 1 condenser 14 will be charged quickly to practi cally the. full voltage of the batteries 16,. or 17,

the rate at which this occurs being controlled chiefly. by a relatively small resistance 22"which may be of the order of "a few hundred ohms. The resistance 9 is suificientlylarge so that the time constant of the condenser circuit does' not permit appreciable discharge of the condenser during the time'that the moving member- 21 is traveling from one positionto the other, and as a result the grid of thetube 6 is mainained at substantially constant potential during this '1 or in common, by placing them near the resist- PATE T oFF-lcEfance 22.] Such impedances may pbe for the purpose of reducing the spark which may occur when the element 21 makes contact on the one side or the other. The networks may take on a variety of forms such as shown in Figs. 3 and 4, Where in one case it is shown as an inductance, and in another case as an inductance in parallel with a vcondenser. Obviously, these networks if used, may take on a large variety or" other forms in accordance with the function which they are intended to perform. In Fig. 1 the platecircuit of the tube 6 may be connected directly to'the line or may be associated therewith by means of a transformer T as shown,.and at the remote end there would be connected anysuitabletypeof receiver R. p I

In Fig. 2 there is shown a modification of the circuit of Fig. 1 adapted for D. C. signaling. In

this case the'same resistances 8, 9 and 22 are shown, and the biasing batteries 11, 16 and 17. There is also shown" thecondenser l4. In'this case, directcurrent signals are sent out over the transmission line,'and the voltages of the bat-' teries 11, 16 and l? are so chosen that when the sending device is at spacing position the plate current of the tube is reduced to zero, but when at marking position normal currentwilhfiow through the plate circuit and the line. ,Here

. again, condenser 14 operates to maintain the potential or" the grid of the tube substantially con-. stant' during the'time of travel of the sending device so that when the member 21 leaves spacing position, having broughtrthe grid potential to blocking value, this potential persists until the member 21 actually makes marking contact,

whereupon the potential of the grid issuddenly raised and the charge on the condenser li isreversed When the element 21 leaves marking position to go to spacing position, again the'con "potential, atransinitting key and a vacuum tube device, means for biasing the grid circuit of the tube by the transmitting key in'accordance with the marking and spacing position of the key, and means associated with the grid circuit to maintain thepotential of the grid substantially con-- stant while the key is between contacts.

2 .'In' a telegraph signaling system a transmission line and a source of voltage, a vacuum tube to the output of which is connected the transmission line and to the input of which is connected the source of voltage, a sending device and means controlled thereby to bias the grid circuit permitting the flow of current in the line when the transmitter is in marking or spacing position and stopping the how when the transmitter is in the reverse position, and means to maintain the grid bias substantially constant during the travel time of the sending device.

3'. In. acarrier frequency telegraph circuit a transmission line and a source of carrier fre quency, a vacuum tube to the output of which is connected the transmission line and to the input of which is. connected the source of carrier transmitter is in marking position and stopping the flow when the transmitter'is in spacingposi- I flow of alternating current in the line when the I tion, and means to'maintain the grid bias sub stantially constant during the travel-timeof the sending device. a v

4. In a carrier frequency telegraph circuit a transmission line and a source of carrier fre-- quency, a three electrode vacuum tube to the output of which is connected the transmissionline and to the input of which is connected the source of carrier frequency, a sending device with a vibrating member, sources of direct current voltage controlled-thereby to bias the grid circuit of the tube in accordance with the signal to be 6. In a carrier frequency telegraph circuit a transmission "line and a source of carrienfre quency, a three-electrode vacuum tube to the output of 'which-is connected the transmission line and to the input of which is connected the source of carrier frequency, a sending device with a vibrating member, oppositely poled sources of direct current voltage, a high resistance concondenser to bias the grid and maintain its potential substantially constant during the travel timeoi the sending device. j JOHN L. CLARKE. 

